By Alister Doyle, Environment Correspondent

OSLO, Oct 13 (Reuters) - Higher levels of pollution in Asia may affect the formation of clouds high in the Himalayas, perhaps disrupting monsoons and speeding a thaw of glaciers, according to a study on Monday.

The report, by scientists in France and Italy, found microscopic particles in the air that can be seeds for water droplets at a Nepalese mountain observatory, the highest in the world at 5,079 metres (16,660 ft) above sea level.

It was the first time scientists had observed such particles forming so high, far above those seen in previous studies from Europe and Japan.

"We think it's because there's a lot of pollution in the valleys which rises and meets clean air masses higher up. This creates new particles," Karine Sellegri at the Universite Blaise Pascal in France, one of the authors, told Reuters.

The study, in the U.S. journal Proceedings of the National Academy of Sciences, said the particles might come from smoke from people burning wood in Himalayan valleys. Or some might have a natural origin, from vegetation.

Still, the scientists pointed to wider risks of the cloud-forming mechanism.

"Rising air pollution levels in South Asia will have worldwide environmental consequences," they wrote.

"Transport of pollutants from the densely populated regions of India, Pakistan, China and Nepal to the Himalayas may lead to substantial radiative forcing (warming effect) in South Asia."

In turn, that could affect the formation of monsoons, disrupt the regional climate and have "dramatic impacts on glacier retreat" in the Himalayas, they wrote.

The U.N. Climate Panel said last year that Himalayan glaciers, which feed rivers on which hundreds of millions of people depend, could shrink to 100,000 square kms (38,610 sq miles) by 2030 from 500,000 now because of global warming.

Sellegri added, however, that it was too early to know exactly what impact rising pollution would have in the Himalayas. "We need more modelling," she said. -- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ (Editing by Louise Ireland)

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